Scientists spot supernova before it blows

Kate Taylor, 6th August 2012

This type of supernova is believed to be the thermonuclear explosion of a white dwarf star that's part of a binary system - two nearby stars that orbit around a common centre of mass. The white dwarf gradually receives mass from its companion and, when its mass eventually reaches 1.4 times that of the sun, explodes to produce a type Ia supernova.

While scientists found thousands of candidate systems that could become type Ia supernovae, none has yet been observed to produce an explosion. Recent studies have found that sodium gas is associated with type Ia supernovae, perhaps because it's ejected from the binary's donor star and lingers around the system. However, Stella Kafka still compares the search to "looking for a needle in a stellar haystack."

Now, though, she and her team have looked at these gas signatures and were able to identify a binary star called QU Carinae as a possible supernova progenitor. It contains a white dwarf, which is accumulating mass from a giant star, and sodium has been detected around the system.

This star belongs to a small category of binaries that are very bright and in which the white dwarf accretes material from its companion particularly quickly. Sodium should be produced in the atmosphere of the mass-donor giant star, and ejected from the system via a stellar wind.

If the white dwarf of this binary explodes into a supernova, she says, the sodium would be detected with the same sort of signature as those found in other type Ia supernovae.

"We are really excited to have identified such a system," says Kafka.

"Understanding these systems, the nature of the two stars, the manner in which mass is exchanged, and their long-term evolution will give us a comprehensive picture on how binaries can create one of the most important explosions in the universe."